The development of new wireless communication systems in the microwave and millimeter-wave bands have spurred the design of new types of compact, wideband, efficient, and low-cost antennas and antenna arrays. Among these, antennas manufactured by printed circuit technology have been increasingly widely used, because they are compact and low-cost. The tapered slot antenna (hereinafter TSA) is one such example, which has become an accepted and popular low cost antenna over the last three decades.
One typical example of such a TSA is shown in FIG. 1, described as prior art in U.S. Pat. No. 5,036,335 to H. L. Jairam for “Tapered Slot Antenna with Balun Slot Line and Stripline Feed”. FIG. 1 shows an exponentially tapered slot (Vivaldi) antenna 10 defined by a metalized layer 15 on one main face of a substrate 14. The antenna 10 has a conventional feed arrangement comprising a microstrip defined by a narrow conductor 11 located on the reverse face of the substrate 14 to that of the tapered slot, and a slotline 13 extending from the narrower end of the slot antenna 10, formed orthogonally to the microstrip. The microstrip and slotline cross each other at right angles, forming an impedance matching balun 18, which is hereinafter known as the microstrip-to-slot transition area, or MST. The microstrip 11 terminates in an open-circuit and extends beyond the slotline 13 by a distance λm/4, where λm is the guide wavelength in the microstrip 11 at the operating frequency of the antenna. The slotline 13 terminates in a short circuit through to the metalized layer 15, extending beyond the microstrip 11 by a distance λs/4, where λs is the guide wavelength in the slotline 11 at the operating frequency of the antenna. Thus, at the cross-over point, the microstrip 11 is effectively short-circuited and the slotline 13 is effectively open-circuited. This form of MST has an inherent narrow bandwidth characteristic, such that the use of the antenna may be limited.
In these antennas, the choice of the substrate material may greatly affect the antenna efficiency. Previously used low temperature co-fired ceramic construction is costly, both from the substrate cost aspect, and from the fabrication costs because of the multilayer process. Liquid crystal polymer (LCP) substrates, with their mechanical flexibility and low permittivity, have been increasingly used for integrated RF and millimeter-wave functions and modules, such as described in the article “3-D-integrated RF and millimeter-wave functions and modules using liquid crystal polymer (LCP) system-on-package technology,” by M. M. Tentzeris et al, published in IEEE Trans. Adv. Packag., vol. 27, no. 2, pp. 332-340, May 2004.
In the 60 GHz band, it is substantially more difficult to achieve wide bandwidths. Some examples of such antennas include wideband 60-GHz annular slot antennas, as described by J. S. Kot, et al, in the article “An integrated wideband circularly-polarized 60 GHz array antenna with low axial-ratio,” in Proc. 2nd Int. Wireless Broadband Ultra-Wideband Commun. Conf., Sydney, Australia, August 2007, and narrowband rectangular patch antennas operating in the 59-61 GHz frequency range as described by L. Amadjikpe, et al, in “Study of a 60 GHz rectangular patch antenna on a flexible LCP substrate for mobile applications,” in IEEE Antennas Propag. Soc. Int. Symp. Dig., San Diego, Calif., July 2008, pp. 1-4. Another 60-GHz antenna, of the linearly tapered slot type, with a wider bandwidth (5.6 GHz around 62 GHz) has also been recently proposed in the article entitled “A compact conformal end-fire antenna for 60 GHz applications,” by L. Amadjikpe et al, published in IEEE Antennas Propag. Soc. Int. Symp. Dig., June 2009, pp. 1-4. A schematic rendering of such a TSA 20 is shown in FIG. 2, where the orthogonal crossing in the MST 22 is shown. Instead of the λm/4 open-circuited stub to provide the maximum field at the cross-over, as shown in the example of FIG. 1, in this implementation, a circle-shaped stub 24 is provided for wider bandwidth characteristics. The other details of the antenna are labeled with the same reference characters as those of FIG. 1. U.S. Pat. No. 6,075,493 to S. Sugawara et al also describes a 60 GHz. TSA.
However, there still exists a need for a compact, wideband TSA construction which overcomes at least some of the disadvantages of prior art antennas.
The disclosures of each of the publications mentioned in this section and in other sections of the specification, are hereby incorporated by reference, each in its entirety.